Is this just UA giving you too many choices and your flights are not listed or just no results?

If it is too many choices the below may help.

I don't know if you are searching mobile or desktop but I have much better success on my desktop. I also recommend trying to play with the advanced search settings. For instance select departure time the hour the XXX flight leaves then list FRA as a connection city. Happy to help you look further if you shoot me a DM

Calling did not help. Apparently, LH is withholding a lot of award inventory from UA:
https://thepointsguy.com/news/luftha...okable-united/
(sorry about the TPG link)

I can confirm this is an ongoing issue. Just booked an award for a client yesterday which was available with Aeroplan, but not with Mileage Plus.

Having raised redemption rates to the stratosphere, United is now trying to cut their costs on the back end by blocking inventory. Starnet blocking was a staple of US Airways and Scott Kirby is at the helm of United, so I'd personally expect more of this.

So some partial blocking is fairly well confirmed but the question is who is blocking who?
Or this a new technology issue?
And why some flights but not others? Is there a pattern?

Hopefully this is resolved soon